This invention relates to antennas, weather radar antennas, and specifically to dual-mode switched aperture array antenna.
A weather radar antenna typically comprises a two dimensional array of radiating elements such as linear waveguides as shown in U.S. Pat. No. 5,198,828 incorporated herein by reference. A typical weather radar antenna provides a pencil or sum beam that is scanned either by physically rotating the antenna or by using phased array techniques known in the art. To form the antenna beam, the entire antenna is fed with a radar signal.
Multi-mode weather radars are being developed and utilized for such applications as obstacle detection, non-operative collision avoidance, controlled flight into terrain (CFIT) avoidance, and terrain imaging and mapping at weather radar frequencies. These multi-mode weather radars require increased resolution to detect obstacles and for imaging. A typical 28-inch diameter weather radar antenna has a 3.5xc2x0 physical 3-dB beam width. Targets cannot be differentiated within the 3-dB beam width. Beam sharpening of the normal weather radar antenna beam is required to further increase resolution for obstade detection.
A military APG-241 radar has been developed that utilizes sub-beam width ground mapping using multi-channel algorithms. This radar is a multi-channel xcexa3/xcex94 monopulse radar. Extensive use of microwave hardware is utilized to develop the needed beam width of the antenna that has resulted in an expensive solution for commercial applications.
An effective beam sharpening factor of seven in one dimension has been previously demonstrated on a previous NASA Task 14 radar contract (contract number NAS1-19704). However an antenna feed network utilized in this approach provided excessive Insertion loss that severely limited the radar range at which beam sharpening was accomplished for single axis sharpening. The Task 14 approach is impractical for two-axis sharpening.
Increased resolution of a weather radar system for obstacle detection has been realized by a switched aperture algorithm. The switched aperture algorithm is a hybrid of sequential lobing and phased-based monopulse. Sub-beam width target features manifest themselves as changes in phase after Doppler shifts are processed out of the radar returns. Using the switched aperture algorithm, a factor of seven effective beam width reduction has been demonstrated under the NASA Task 14 contract previously mentioned. In order to demonstrate the switched aperture algorithm, an implementation under the NASA contract used commercial of the shelf (COTS) single pole double throw (SPDT) X-band microwave switches. The proof-of-concept demo was for a single axis implementation. Using the COTS switches resulted in marginal range of the radar due to sever insertion losses. The COTS switches also had power handling concerns. Implementation of a two-axis switched aperture is not practical using COTS switches due to insertion losses.
What is needed is a high performance, low-loss, dual-mode, simple and practical antenna feed switching network design for a switched aperture beam sharpening algorithm that also may be used as a sum beam for conventional weather detection.
An antenna having a dual-mode switched aperture antenna feed for feeding an input signal to selected portions of the antenna to form a desired beam is disclosed. The antenna feed comprises an input divider for receiving the input signal and splitting the input signal. A left switch receives the split input signal and switches the split input signal to selected portions of the antenna. The left switch further comprises a left first diode and a left second diode for switching the split input signal. A right switch receives the split input signal and switches the split input signal to selected portions of the antenna. The right switch further comprises a right first diode and a right second diode for switching the split input signal.
In the left switch when the first diode is reversed biased and the second diode is forwarded biased the left switch is a waveguide elbow from an input port to a first output port and the signal is applied to a first portion the antenna. When the first diode is forward biased and the second diode is reverse biased the left switch is a waveguide elbow from the input port to a second output port and the signal is applied to a second portion of the antenna.
In the right switch when the right first diode is reversed biased and the right second diode is forwarded biased the right switch is a waveguide elbow from an input port to first output port and the signal is applied to a third portion of the antenna. When the right second diode is reversed biased and right first diode is forwarded biased the right switch is a waveguide elbow from the input port to a second output port and the signal is applied to a fourth portion of the antenna.
A desired beam of the antenna is formed by feeding the split input signal to a top portion of the antenna by reverse biasing the left first diode and forward biasing the left second diode to feed the split input signal to a top left (TL) quadrant of the antenna and by forward biasing the right first diode and reverse biasing the right second diode to feed the split input signal to a top right (TR) quadrant of the antenna.
A desired beam of the antenna is formed by feeding the split input signal to a bottom portion of the antenna by forward biasing the left first diode and reverse biasing the left second diode to feed the split input signal to a bottom right (BR) quadrant of the antenna and by reverse biasing the right first diode and forward biasing the right second diode to feed the split input signal to a bottom left (BL) quadrant of the antenna.
A desired beam of the antenna is formed by feeding the split input signal to a left portion of the antenna by reverse biasing the left first diode and forward biasing the left second diode to feed the split input signal to a TL quadrant of the antenna and by reverse biasing the right first diode and forward biasing the right second diode to feed the split input signal to the BL quadrant of the antenna.
A desired beam of the antenna is formed by feeding the split input signal to a right portion of the antenna by forward biasing the left first diode and reverse biasing the left second diode to feed the split input signal to the BR quadrant of the antenna and by forward biasing the right first diode and reverse biasing the right second diode to feed the split input signal to the TR quadrant of the antenna.
A desired beam of the antenna is formed by feeding all portions of the antenna by reverse biasing the left first diode, the left second diode, the right first diode, and the right second diode to feed the split signals to the TL, TR, BL, and BR quadrants of said antenna.
It is an object of the present invention to provide a high-performance dual-mode simple and practical antenna feed switching network design for a switched aperture beam sharpening algorithm that also may be used as a sum beam for conventional weather detection.
It is an object of the present invention to provide a two-axis switching network with reduced losses.
It is an advantage of the present invention to provide a dual-mode antenna feed switching network that uses low-cost waveguide components.
It is an advantage of the present invention to provide a switching network that is lighter than previous networks.
It is a feature of the present invention to provide a dual-mode switched aperture antenna for aircraft applications that can be used for weather radar, collision avoidance, object mapping and imaging purposes.
It is a feature of the present invention to provide a dual-mode switched aperture antenna for next generation multimode weather radar system applications.